No abstract

Insulators regulate transcription as they modulate the interactions between enhancers and promoters by organizing the chromatin into distinct domains. To gain better understanding of the nature of chromatin domains defined by insulators, we analyzed the ability of an insulator to interfere in VDJ recombination, a process that is critically dependent on long-range interactions between diverse types of cis-acting DNA elements. A well-established CTCF-dependent transcriptional insulator, H19 imprint control region (H19-ICR), was inserted in the mouse TCRβ locus by genetic manipulation. Analysis of the mutant mice demonstrated that the insulator retains its CTCF and position-dependent enhancer-blocking potential in this heterologous context in vivo. Remarkably, the inserted H19-ICR appears to have the ability to modulate cis-DNA interactions between recombination signal sequence elements of the TCRβ locus leading to a dramatically altered usage of Vβ segments for Vβ-to-DβJβ recombination in the mutant mice. This reveals a novel ability of CTCF to govern long range cis-DNA interactions other than enhancer–promoter interactions and suggests that CTCF-dependent insulators may play a diverse and complex role in genome organization beyond transcriptional control. Our functional analysis of mutated TCRβ locus supports the emerging role of CTCF in governing VDJ recombination.

A number of studies in the recent past have proposed a variety of scaling relationships among the penetration depth at the bottom of a convective region, the vertical velocity of the Ñuid and theWhile a relationship of the form has been proposed by Schmitt and coworkers (F b ). * d P V z 3@2 on the basis of the equations of motion for buoyant plumes, Zahn proposed a similar relationship based on scaling arguments. The relationships involving and the input Ñux are based on recent two-* d , V z , dimensional numerical simulations by Hurlburt and coworkers. All these scalings were recently looked into by Singh, Roxburgh, & Chan, who performed full three-dimensional simulations of turbulent compressible convection for a stable-unstable-stable sandwich conÐguration. In the present study, we numerically solve the full set of Navier-Stokes equations in three dimensions in order to study the behavior of convective motions penetrating into the bottom stable layer. We take up a series of models di †ering in resolution or mesh size and aspect ratio with a view to examine, in greater detail, the scaling relationships between the penetration distance and other Ñow parameters.

Understanding the molecular basis of monoallelic expression as observed at imprinted loci is helpful in understanding the mechanisms underlying epigenetic regulation. Genomic imprinting begins during gametogenesis with the establishment of epigenetic marks on the chromosomes such that paternal and maternal chromosomes are rendered distinct. During embryonic development, the primary imprint can lead to generation of secondary epigenetic modifications (secondary imprints) of the chromosomes. Eventually, either the primary imprints or the secondary imprints interfere with transcription, leading to parent-of-origin-dependent silencing of one of the two alleles. Here we investigated several aspects pertaining to the generation and functional necessity of secondary methylation imprints at the Igf2/H19 locus. At the H19 locus, these secondary imprints are, in fact, the signals mediating paternal chromosome-specific silencing of that gene. We first demonstrated that the H19 secondary methylation imprints are entirely stable through multiple cell divisions, even in the absence of the primary imprint. Second, we generated mouse mutations to determine which DNA sequences are important in mediating establishment and maintenance of the silent state of the paternal H19 allele. Finally, we analyzed the dependence of the methylation of Igf2DMR1 region on the primary methylation imprint about 90 kilobases away.